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Smart Contract Functionality

Overview​

The New Horizen Smart Contract is deployed on Ethereum, where it receives an attestation from the New Horizen authorized relayer.

Storage Variables​

The New Horizen Smart Contract keeps the attestations as storage variables:

mapping(uint256 => bytes32) public proofsAttestations;

Methods​

Submit Attestation Method​

function submitAttestation(
   uint256 _attestationId,
   bytes32 _proofsAttestation
)external onlyRole(ADMIN);
  • Verifies that the attestation id is incremental (newAttestationId = latestAttestationId + 1) if and only if this check is enabled.
  • Adds a new entry to the mapping using the newAttestationId and storing the newAttestation.
  • Emits a new AttestationPosted(attestationId, attestation) event.

Submit Attestations Batch Method​

This method is used in the situation when multiple attestations have been published on New Horizen while the relayer is down but recovers later on.

function submitAttestationsBatch(
   uint256[] _attestationIds,
   bytes32[] _proofsAttestations
)external onlyRole(ADMIN);
  • Checks that _attestationIds.len() == _proofsAttestations.len().
  • Invokes the submitAttestation method multiple times.

It’s a bit cheaper than calling submitAttestation externally multiple times, as you’ll pay the initial gas fee only one time. Additionally, it avoids edge cases related to Ethereum nonce management.

Verify Proof Attestation Method​

This method is used by proof submitters’ contracts to verify that their proof has been attested by a published attestation.

function verifyProofAttestation(
      uint256 _attestationId,
      bytes32 _leaf,
      bytes calldata _merklePath,
      uint32 _number_of_leaves,
      uint256 _index
   ) external view returns (bool)
  • Checks _attestationId exists in the proofsAttestations storage mapping.
  • Computes claimedAttestation = apply(_leaf, _merklePath, _index).
  • Returns claimedAttestation == proofsAttestation[_attestationId].

The verification of the Merkle path is carried out by employing the Merkle.sol library contract provided by EigenDA. We preferred this choice over OpenZeppelin, as it is assuming that both leaves and internal nodes are ordered lexicographically, which is something not necessarily true for us. Moreover, EigenDA implementation is more optimized.

However, such implementation needs to be modified to accommodate the fact that Substrate uses a slightly optimized version of a Binary Merkle tree, while the contract assumes the Merkle tree to be always complete and balanced. Please refer to the Substrate source code for more info.